A conventional heat pack used for therapeutic use is a hot water bottle. While modern hot water bottles, which are made of rubber, are flexible they have the major disadvantage that they must be filled with hot water, which is usually at a temperature at or nearing boiling point. This is dangerous, particularly for children, the elderly, and persons with impaired movement or vision.
To overcome the aforementioned disadvantage, gel packs have been developed which can be heated, typically in a microwave oven, and used therapeutically. However, these tend to be expensive and hazardous in the case of a leak.
U.S. Pat. No. 4,765,338 discloses a heating or cooling pack for the entire scalp. The pack has been particularly developed for use as a cooling pack by patients undergoing chemotherapy treatment and has not been designed primarily as a heat pack, unlike the present invention.
U.S. Pat. No. 5,447,532 describes a water pillow or "ice bag" which comprises a closed bag made of a cloth or nonwoven fabric that has a high water permeability and that contains a water absorptive high polymer material, i.e. a gelling material. This pack has again been designed for use primarily as a cool pack.
Other conventional heat packs comprise electric blankets and pads, and devices using exothermic chemical and physical reactions. These types of apparatus tend to to be expensive to produce and/or to operate. In addition, those dependent on exothermic reactions can be unreliable and may not be sufficiently flexible in their heat-producing state to be able to mould themselves to a part of the body to be treated.
Variations on all these products have also been produced for use on inanimate objects but usually exhibit the same disadvantages as aforesaid.
The object of the present invention is to provide a heat pack which overcomes or substantially mitigates the aforementioned disadvantages and which is inexpensive and safe to use.
According to the present invention there is provided a heat pack for being heated to at least 55.degree. C. and comprising a flexible, impervious outer container which is adapted to be sealed to retain a liquid therein and of maintaining its sealed integrity when heated to at least 55.degree. .C and which contains a porous, non-rigid filling material and a predetermined quantity of a preservative at a concentration that inhibits microbial growth within the liquid-filled container when sealed, and characterised in that the filling material comprises at least one of a woven textile material, a nonwoven fabric, a sponge-like material, and paper, which filling material absorbs at least its own weight of said liquid.
For convenience and safety, the liquid used in the heat pack may be water. It will be appreciated, however, that the heat pack if not already supplied to the end-user in a water-filled, sealed condition, can be filled with cold water and sealed before being heated. The liquid within the container is absorbed by the porous filling material, which in addition to imparting a degree of rigidity to the heat pack is advantageous from a safety point of view after the heat pack has been heated should the outer container be ruptured.
The container may comprise a resealable bag or a sealed bag with a valve permitting it to be emptied, filled or topped up with liquid as desired.
It will be appreciated that when the pack is heated any air trapped inside the pack will expand. In extreme circumstances this can exacerbate expansion of the pack causing rupture. Hence, preferably, air is removed from the outer container prior to it being sealed. Advantageously, therefore, the valve permits air to be removed from the container after it has been filled with the liquid.
Alternatively, the container may be permanently sealed after the addition of water or other liquid and the removal of air therefrom, and may be supplied to the end user ready for use in this condition.